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2. Carbonyl Compounds
3. Natural Products
4. Carbonyl Structure Carbon is sp2 hybridized.
C=O bond is shorter, stronger, and more polar than C=C bond in alkenes.
5. IUPAC Names for Ketones Replace -e with -one. Indicate the position of the carbonyl with a number.
Number the chain so that carbonyl carbon has the lowest number.
For cyclic ketones the carbonyl carbon is assigned the number 1. =>
6. Examples
7. Naming Aldehydes IUPAC: Replace -e with -al.
The aldehyde carbon is number 1.
If -CHO is attached to a ring, use the suffix -carbaldehyde. =>
8. Examples
9. Name as Substituent On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl.
Aldehyde priority is higher than ketone.
11. http://www.cem.msu.edu/~reusch/VirtTxtJml/aldket1.htm
12. Chapter 18 12 http://www.cem.msu.edu/~reusch/VirtTxtJml/aldket1.htm
14. Chapter 18 14
25. Chapter 18 25
26. Chapter 18 26
27. Chapter 18 27
29. Figure: 18-07-67Summ
Caption:
Nucleophiles can add under acidic or basic conditions to carbonyl groups.
Figure: 18-07-67Summ
Caption:
Nucleophiles can add under acidic or basic conditions to carbonyl groups.
32. Addition of Water In acid, water is the nucleophile.
In base, hydroxide is the nucleophile.
Aldehydes are more electrophilic since they have fewer e--donating alkyl groups.
33. Figure: 18-07-79UN
Caption:
Hydration occurs through the nucleophilic addition mechanims, with water (in acid) or hydroxide (in base) serving as the nucleophile.
Figure: 18-07-79UN
Caption:
Hydration occurs through the nucleophilic addition mechanims, with water (in acid) or hydroxide (in base) serving as the nucleophile.
34. Figure: 18-07-70UN
Caption:
The ylide attacks a carbonyl carbon to give a charge separated intermediate called a betaine. Phosphorus and oxygen form strong bonds, and the attraction of opposite charges promotes the fast formation of a four-membered oxaphosphetane ring. The ring quickly collapses to give the alkene and triphenylphosphine oxide.
Figure: 18-07-70UN
Caption:
The ylide attacks a carbonyl carbon to give a charge separated intermediate called a betaine. Phosphorus and oxygen form strong bonds, and the attraction of opposite charges promotes the fast formation of a four-membered oxaphosphetane ring. The ring quickly collapses to give the alkene and triphenylphosphine oxide.
35. Addition of HCN HCN is highly toxic.
Use NaCN or KCN in base to add cyanide, then protonate to add H.
Reactivity formaldehyde > aldehydes > ketones >> bulky ketones.
44. Formation of Imines Nucleophilic addition of ammonia or primary amine, followed by elimination of water molecule.
C=O becomes C=N-R
Condensation reaction
46. pH Dependence Loss of water is acid catalyzed, but acid destroys nucleophiles.
NH3 + H+ ?? NH4+ (not nucleophilic)
Optimum pH is around 4.5 =>
47. Other Condensations
57. Wittig Reaction Nucleophilic addition of phosphorus ylides. C=O becomes C=C.
66. Acetals as Protecting Groups
67. Oxidation of Aldehydes Easily oxidized to carboxylic acids.
68. Tollens Test Add ammonia solution to AgNO3 solution until precipitate dissolves.
Aldehyde reaction forms a silver mirror.
69. Reduction Reagents Sodium borohydride, NaBH4, reduces C=O, but not C=C.
Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle.
Hydrogen gas with catalyst also reduces the C=C bond. =>
70. Catalytic Hydrogenation Widely used in industry.
Raney nickel, finely divided Ni powder saturated with hydrogen gas.
Pt and Rh also used as catalysts.
71. Deoxygenation Reduction of C=O to CH2
Two methods:
Clemmensen reduction if molecule is stable in hot acid.
Wolff-Kishner reduction if molecule is stable in very strong base. =>
72. Clemmensen Reduction
73. Wolff-Kisher Reduction Form hydrazone, then heat with strong base like KOH or potassium t-butoxide.
Use a high-boiling solvent: ethylene glycol, diethylene glycol, or DMSO.
74. IR Spectroscopy Very strong C=O stretch around 1710 cm-1.
Conjugation lowers frequency.
Ring strain raises frequency.
Additional C-H stretch for aldehyde: two absorptions at 2710 cm-1 and 2810 cm-1. =>
75. 1H NMR Spectroscopy
76. 13C NMR Spectroscopy
77. MS for 2-Butanone
78. MS for Butyraldehyde
79. McLafferty Rearrangement Loss of alkene (even mass number)
Must have ?-hydrogen
80. UV Spectra, ? ? ?* C=O conjugated with another double bond.
Large molar absorptivities (> 5000)
81. UV Spectra, n ? ?* Small molar absorptivity.
Forbidden transition occurs less frequently.
82. End of Chapter 18
